As a conventional material in the microelectronics field, a silicon material has absolute advantages for a processing technology and manufacturing costs. However, a conventional interconnection solution based on a metallic wire and a dielectric is limited by a delay, power consumption, bandwidth, and the like, and it is difficult to meet a global requirement of a future many-core system on chip. Compared with electrical interconnection, optical interconnection has advantages such as high bandwidth, low power consumption, and a short delay, and is expected to comprehensively resolve a current problem faced by the electrical interconnection. In recent years, silicon-based optical interconnection has received extensive attention from researchers, and develops rapidly. A silicon-based modulator is one of basic components in a silicon-based optical interconnection technology, and is an important research topic in recent years. Common silicon-based modulators include a modulator based on a free-carrier dispersion effect and a modulator based on electro-absorption.
The modulator based on the free-carrier dispersion effect means that a voltage is applied to a silicon modulation area to cause a distribution change of carriers inside silicon. Due to the free-carrier dispersion effect, a refractive index of light in the silicon also changes, such that an optical signal is modulated. Currently, the modulator based on the free-carrier dispersion effect mainly falls into two types: a silicon Mach-Zehnder interferometer (MZI) modulator, which has advantages such as a higher modulation rate and higher optical bandwidth and disadvantages such as a large size, large power consumption, and a required traveling wave; and a silicon microring modulator, which has advantages such as a small size and a high modulation rate and disadvantages such as extremely sensitivity to temperature, low modulation bandwidth, a small technology tolerance, and poor applicability.
The modulator based on electro-absorption refers to an optical signal modulation component that is manufactured using an electro-optic effect (Franz-Keldysh effect) in a semiconductor, which has advantages such as high modulation bandwidth, low power consumption, practical optical bandwidth, and an acceptable extinction ratio. However, because silicon has a poor electro-optic effect, a second material needs to be introduced and doped into silicon for improvement. A germanium material has a significant electro-optic effect in a C band (1550 nm), and is fully compatible with a conventional complementary metal-oxide-semiconductor (CMOS) technology. Therefore, one promising alternative solution is to use germanium as the second material to manufacture a germanium or silicon-germanium electro-absorption modulator.
The germanium or silicon-germanium modulator has advantages such as a small size, low power consumption, and a high modulation rate. A main topic of this type of modulator is coupling between a germanium or silicon-germanium modulation area and a silicon-based waveguide. Currently, there are mainly two coupling manners. One manner is that the germanium or silicon-germanium modulation area is directly coupled to the silicon-based waveguide by means of alignment. However, because silicon and germanium have different refractive indexes, the manner of direct coupling by means of alignment has end surface reflection, which causes a coupling loss. Further, in a current manufacturing method, a PIN junction is manufactured on the germanium modulation area, which causes light absorption in a doping area, and causes an absorption loss. In addition, the manner of direct coupling by means of alignment has a complex manufacturing technology, and is difficult to implement. The other manner is to perform coupling using an evanescent wave. This type of coupling structure includes a structure of a horizontal PIN junction proposed by the IME in Singapore and a structure of a vertical PIN junction proposed by the Institute of Semiconductors, Chinese Academy of Sciences. For the structure of the horizontal PIN junction proposed by the IME, because a propagation length required for mode field stability is not considered, a propagation loss is large; and because the PIN junction is manufactured on the germanium modulation area, an absorption loss exists. The structure of the vertical PIN junction proposed by the Institute of Semiconductors, Chinese Academy of Sciences has a complex manufacturing technology, and requires technologies such as multiple times of growing, etching, and doping. In addition, to easily manufacture a structure of n++ Si, the silicon-germanium modulation area is wide, and the modulation area has multiple modes, which affects a communication capacity and a transmission distance.